1. Field of the Invention
Aspects of the invention relate to a switched-mode power supply and a power supply method thereof, and more particularly to a switched-mode power supply capable of indicating a voltage of an output power and a power supplying method thereof.
2. Description of the Related Art
A switched-mode power supply rectifies alternating current (AC) power received from an external power source to obtain direct current (DC) power, converts the DC power by performing a switching operation, changes a voltage of the AC power using a transformer, and rectifies and smoothes the transformed AC power, thereby outputting smoothed DC power. However, the transformer may be omitted, and the level of the output DC power may be controlled by controlling the duty cycle of the switching operation. Such a switched-mode power supply has achieved widespread use because it has a lower power loss and generates less heat compared to a linear power supply that converts AC power into DC power using a passive element, such as a resistor, to reduce a voltage.
FIG. 1A is a block diagram of a switched-mode power supply according to the related art. As shown in FIG. 1A, the switched-mode power supply 1 according to the related art includes a converter 2 to convert input power into output power having a predetermined voltage by performing a switching operation, an output unit 3 to output the output power to an external load (not shown), a light emitting unit 4 to emit light indicative of the voltage of the output power when the voltage of the output power is equal to or greater than a predetermined threshold voltage, a light receiving unit 5 to receive the light emitted from the light emitting unit 4 and output a signal indicative of the voltage of the output power, and a switching controller 6 to control a switching operation of the converter 2 according to the voltage of the output power indicated by the signal output from the light receiving unit 5.
FIG. 1B is a circuit diagram of the switched-mode power supply 1 of FIG. 1 according to the related art. Referring to FIG. 1B, when the light indicative of the voltage of the output power is transmitted from the light emitting unit 4 to the light receiving unit 5, the signal indicative of the voltage of the output power that is output from the light receiving unit 5 is input to a feedback terminal FB of the switching controller 6 to which a capacitor is connected. The capacitor affects a response time of the switching controller 6 to a change in the signal indicative of the voltage of the output power that is output from the light receiving unit 5. The smaller the capacitor, the shorter or faster the response time, and the larger the capacitor, the longer or slower the response time.
However, the capacitor connected to the feedback terminal FB in the switched-mode power supply 1 according to the related art has a fixed value regardless of a size of the load that is receiving the output power from the output unit 3, so that a voltage that is actually applied to the feedback terminal FB of the switching controller 6 as a result of the effect of the capacitor may differ substantially from the signal indicative of the voltage of the output power that is output from the light receiving unit 5 if the load rapidly changes or noise is introduced into the system, thereby causing a malfunction of the switched-mode power supply 1, such as a shutdown, due to an inaccurate voltage being applied to the feedback terminal FB of the switching controller 6.